.. Since Gray had a rap sheet a mile long .... was Freddie Gray in violation of probation due to the possession of a weapon ... in this case a knife?
Since Grey had a long criminal record, it is likely that he was recognized by the officers.
If Grey was recognized as being a convicted felon, likely on parole or probation, possession of a weapon would likely have violated the terms of his probation, and would have generated both probable cause, and also a reason for him to run.
It seems a definate possibility if not a liklihood.
He was also out on bail for an upcoming drug trial.